Increasing The Strength Of Metals And Metal Components

ABSTRACT

A method for increasing the strength of metals or metal components includes selecting a wrought metal or powder metal sample having a mass equal to or greater than a final mass of a component to be formed. If the sample is wrought metal, it is placed in a die cavity and subjected to high velocity adiabatic impact that forms a component having greater mechanical strength than the original wrought metal sample. If the sample is powder metal, it is placed in a die cavity and subjected to high velocity adiabatic impact to form a green preform that is sintered in a substantially oxygen free environment to form a sintered preform. The sintered preform has greater mechanical strength than a conventional wrought metal sample of the same material. The sintered preform may be optionally placed in a final die cavity and subjected to high velocity adiabatic impact to form a component.

BACKGROUND

1. Field

The present disclosure relates to metallurgy. More particularly, the disclosure concerns production methods of forming wrought metals and processes for compacting power metals.

2. Description of the Prior Art

By way of background, the mechanical strength of metals and metal components is presently limited by the production methods of forming wrought metals and powder metal techniques. Mechanical strength as used herein includes one or more strength factors such as yield strength, ultimate tensile strength, fatigue strength, etc.

Existing wrought metal manufacturing methods involve some type of pressure rolling in hot or cold form. Powder metal (PM) parts are processed today through a combination of techniques of isostatic pressing, long sintering times, and hot isostatic pressing (HIP), and at best provide metal components of equal strength to metal components manufactured from wrought metals using traditional methods, including lathes, mills, forming presses, etc.

The design practices for metal components to survive and perform adequately under real world loads involve selecting component sizes that, combined with the given strength properties, will provide desired performance and cycle life. Today, if higher loads are required to be withstood, part sizes are accordingly increased. There is a constant trade-off in the metal component design process of part size and design loads the part can adequately handle. If additional strength could be obtained from a given metal, that metal could be used in the design of metal components without resorting to the use of different more expensive stronger metals. Many products such as car engines, jet engines, orthopedic components and others could be made lighter and less expensively and still meet load requirements.

The challenges associated with manufacturing metal components made from wrought metals or powder metals begin with the limitations of component strength that can be achieved through current raw metal manufacturing methods. In addition, there is often a need for multiple manufacturing operations to provide the dimensional accuracy and precision required for a given component. For example, manufacturing an orthopedic knee implant typically requires the steps of casting the metal, machining, grinding and polishing the final product. An automotive engine connecting rod made from powder metal typically requires the steps of low temperature isostatic pressing, sintering for twelve hours or more, and several minutes of hot isostatic pressing.

The present disclosure addresses the foregoing concerns by providing significantly stronger metal components while providing cost reductions due to high processing speeds.

SUMMARY

A method for increasing the strength of metals or metal components is disclosed. A wrought metal sample or a powder metal sample. The sample has a mass equal to or greater than a final mass of a component to be formed.

If the sample is a wrought metal sample, it is placed in a die cavity incorporating geometric features of the component to be formed. The wrought metal sample in the die cavity is subjected to high velocity adiabatic impact. The high velocity adiabatic impact forms the wrought metal sample into a component having greater mechanical strength than the wrought metal sample prior to receiving the high velocity adiabatic impact.

If the sample is a powder metal sample, it is placed in a die cavity incorporating geometric features of a green preform to be created. The powder metal sample in the die cavity is subjected to high velocity adiabatic impact to form the green preform. The green preform is sintered in a substantially oxygen free environment to form a sintered preform. The sintered preform has greater mechanical strength than a wrought metal sample of the same material that has not received high velocity adiabatic impact. The sintered preform may be optionally placed in a final die cavity and subjected to high velocity adiabatic impact to form a component.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying Drawings, in which:

FIG. 1 is a graph comparing tensile strength for wrought ingot and powder metal samples of Ti64 titanium alloy using conventional processing versus processing performed in accordance with the present disclosure; and

FIG. 2 is a graph comparing tensile strength for wrought ingot and powder metal samples of Ti CP-2 unalloyed titanium using conventional processing versus processing performed in accordance with the present disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Applicant has determined that significantly stronger metals and metal components can be produced using high velocity adiabatic impact (HVAI) for wrought metals and a combination of HVAI and post-compaction sintering for power metals. This will enable smaller, lighter metal components that can withstand a given load, or enable improved product performance and cycle life for a given part size. The methods disclosed herein can be used to produce a myriad of metal components including: gears, engine valves, powertrain components, orthopedic implants (knees, hips, bone screws, trauma plates, etc.), dental implants (bone implants, abutments, etc.), shape charges liners, shape charge cases, fasteners, metal golf club heads, turbine engine stator and rotor blades, projectiles for ordnance such as bullets, cannon projectiles, weapons components such as triggers, springs, body armor, and more.

For components made from wrought metals in the form of bar or rod stock, wire stock, sheet stock, plate stock or blanks, a mass of wrought metal equal to or slightly greater that the final mass of the desired component is cut (e.g., as a slug of cylindrical or other shape) and placed into an HVAI rapid forming press. The metal mass is held in a forming die cavity or a preforming die cavity, which may be either a single die with the desired part features in the die or a dual or split die design incorporating the desired part features. A high velocity ram is used to impact the metal mass through an intermediate punch. The punch receives the high velocity impact from the ram on one end and transfers an impulse and kinetic energy into the metal mass on the other end of the punch. The metal mass is pushed very rapidly into the die cavity and formed. The formed part is then ejected. With ram velocities exceeding 8 meters/second, forming occurs in less than 100 milliseconds, and the metal part is formed with approximately 21% or greater mechanical strength (tensile, ultimate, and other) as compared to the initial wrought metal.

When powder metals are used, the powder metal takes the place of the wrought metal. A powder metal mass that is equal to or slightly larger than the mass of the desired final component is placed into an HVAI rapid forming press. The power metal mass is held in a forming die cavity. A high velocity ram is used to impact the powder metal mass through an intermediate punch. The high velocity impact from the punch compresses the metal powder in excess of 95% of the wrought density of the metal, creating a green preform. After ejecting the green preform from the forming cavity, the preform is sintered with a sintering profile suitable for the metal being used to produce a sintered preform. The total sintering time typically will not exceed six hours, which is less than half the time required for conventional powder metal (PM) sintering. The sintering profile may be implemented with a high vacuum oven with oxygen removed, a controlled rate of temperature increase, a controlled maximum sintering temperature for 1 to 4 hours, and a controlled cooling rate appropriate for the metal being used. The high velocity-impacted sintered metal has strength properties of approximately 27% to 94% higher than conventional wrought metal or powder metal strengths for the same material.

Note that the sintered preform may or may not have a final desired component part shape. If it does not, the sintered preform can be optionally further impacted with HVAI into a final component having a desired part shape at a high rate of production, with as high as several parts per second being possible.

For both wrought metal and powder metal components, the steps are performed in sequential, serial fashion. The previous step is completed before the next step is performed. The preferred process design incorporated into a machine system is as follows:

1. Spring loaded Ram design, return loading of the spring ram after firing the ram via an electric motor utilizing a belt driven design.

2. Punches made of strong steels—tool steels or stronger.

3. Die cavities made of strong steels—tool steels or stronger.

4. Part eject features using mechanical fingers with pneumatic assist.

For both wrought and powder metal components, the following features and elements may be used to create a part with superior strength:

1. Ram velocity of impact greater than 8 meters per second. This is adjusted depending upon the metal being used and the size of the part. A larger part will require more impulse and kinetic energy to form, so higher velocity of impact is required. A stronger metal—i.e., titanium Ti64 versus a low carbon steel, will also require more impulse and kinetic energy for a given mass, so higher impact velocities will be required.

2. Multiple rams can be used to provide the impulse and kinetic energy to the metal mass in order to create components of various design features.

3. The rams can be driven by independently controlled motors with precision controls including servo feedback and variable frequency drives, or cam driven rams driven off of one or more main drives can be used in lieu of independently driven and controlled rams.

4. Whether using independently driven rams or cam driven rams, each axis of impact may have its own punch designed to transfer the impulse and kinetic energy of the ram to the metal mass. However, the use of simple impact of a ram directly onto the metal mass also works.

5. If desired, multiple cavities forming multiple parts off a single HVAI ram or multiple HVAI rams either independently driven and controlled or cam driven are also possible.

For forming parts using powder metals, the combination of rams, ram drives and controls and punches or direct ram impact to the powder metal are the same as those for forming parts with wrought metals. However, to fully gain the desired strength increases the further step of sintering is desired. Once sintered properly, the PM component will gain the large increases in strength mentioned above.

The speed of the process facilitates low cost manufacturing. The feeding of a wrought or powder metal mass, the HVAI impact, and the ejection of the part or green preform all take 2 seconds or less. These processes can be accomplished at the rate of four complete feed-HVAI impact-eject cycles per second or faster.

As noted above, with HVAI forming of powder metals, once the HVAI-compacted green preform has been sintered to produce the sintered preform, an option is to perform additional HVAI on the sintered preform using a final cavity and punch design to form a component having final design features equivalent to forming a wrought metal mass into a final component part. Adding this additional step allows a simpler more robust green preform to be produced by HVAI powder compaction prior to sintering, with the final component shape being produced after sintering.

Test Results

Testing was initiated to compare the tensile strength of titanium test specimens produced from conventional manufacturing processes versus titanium test specimens produced using the above-described HVAI and HVAI/sintering techniques. The test specimens consisted of two grades of titanium, namely, Ti64 titanium alloy and Ti CP-2 unalloyed titanium. Test specimens were produced from both wrought ingots and powder metal samples for the Ti64 material, and from powder metal samples for the Ti CP-2 material.

Conventional wrought metal test specimens were machined from Ti64 and Ti CP-2 materials per ASTM specification. Material samples subjected to HVAI were impacted on an HVAI press manufactured by LMC Inc. of Cortland, Illinois. Two HVAI wrought metal test specimens were produced from Ti64 ingots by first pressing the ingots into sheet form by way of the HVAI operation. The ingots measured 0.42 cm³ and 0.399 cm³ in size and their mass was 1.894 grams and 1.796 grams respectively. The HVAI ram speed was 20 meters/second and the ram/punch mass was 42 kg. The kinetic energy delivered to the samples was 8,560 joules. The wrought metal test specimens were then machined per ASTM specification from the pressed sheet.

The powder metal test specimens were produced by compacting powder metal samples into green preform specimens having the desired ASTM test configuration using HVAI and a suitable forming die cavity. Three samples of raw powder metal for Ti64 measured 0.407 cm³, 0.570 cm³ and 0.615 cm³ in size and their mass was 1.832 grams, 2.570 grams and 2.769 grams, respectively. The HVAI ram speed was 25 meters/second and the ram/punch mass was 42 kg. The kinetic energy delivered to the powder metal was 13,125 joules. Two samples of powder metal for Ti CP2 powder measured 0.436 cm³ and 0.495 cm³ in size and their mass was 1.964 grams and 2.230 grams, respectively. The HVAI ram speed was 25 meters/second and the ram/punch mass was 42 kg. The kinetic energy delivered to the powder metal was 13,125 joules.

The HVAI-compacted green preform specimens were sintered per industry standard in an oxygen-free environment to produce sintered preform specimens representing the final powder metal test specimens. The following time-temperature sintering regime was used:

(i) Approximately 30 minute rise in temperature to 880 deg C.;

(ii) Approximately 1 hour at 880 deg C.;

(iii) Approximately 15 minute rise in temperature to 1260 deg C.;

(iv) Approximately 2 hours at 1260 deg C.;

(v) Furnace cool to room temperature;

(vi) Total cycle time approximately 6 hours.

An advantageous feature of sintering following HVAI is that no isostatic pressing is required before, during or after sintering because very high density (95% and above) is achieved by the HVAI operation prior to sintering.

FIGS. 1 and 2 illustrate the improved tensile strength of the HVAI-processed titanium test specimens. FIG. 1 shows tensile test results for the Ti64 titanium alloy test specimens. A conventional Ti64 wrought metal test specimen is shown on the far left of FIG. 1. Second from the left is a first Ti64 HVAI wrought metal test specimen. Third from the left is a second Ti64 HVAI wrought metal test specimen. Fourth from the left is a first Ti64 HVAI/sintered powder metal test specimen. Fifth from the left is a second Ti64 HVAI/sintered powder metal test specimen. Sixth from the left is a third Ti64 HVAI/sintered powder metal test specimen. The tensile strengths are shown in Table 1 below:

TABLE 1 Ti64 Test Specimen Ingot Powder Conventional Wrought   896 MPa HVAI Wrought #1 1084.4 MPa HVAI Wrought #2 1084.2 MPa HVAI/Sintered Powder #1 1138.3 MPa HVAI/Sintered Powder #2 1154.9 MPa HVAI/Sintered Powder #3 1185.9 MPa

FIG. 1 and Table 1 indicate that the Ti64 HVAI wrought metal test specimens each had approximately 21% greater tensile strength than the conventional Ti64 wrought metal test specimen. The Ti64 HVAI/sintered powder metal test specimens had approximately 27%, 29% and 32%, respectively, greater tensile strength than the conventional wrought metal test specimen.

FIG. 2 shows tensile test results for the Ti-CP2 titanium alloy test specimens. A conventional Ti-CP2 wrought metal test specimen is shown on the left of FIG. 2. Second from the left is a first HVAI/sintered powder metal test specimen. Third from the left is a second HVAI/sintered powder metal test specimen. The tensile strengths are shown in Table 2 below:

TABLE 2 Ti-CP2 Test Specimen Ingot Powder Conventional Wrought 345 MPa HVAI/Sintered Powder #1 669 MPa HVAI/Sintered Powder #2 590 MPa

FIG. 2 and Table 2 indicate that the Ti-CP2 HVAI/sintered powder metal test specimens had approximately 94% and 71%, respectively, greater tensile strength than the conventional Ti-CP2 wrought metal test specimen.

A follow-up analysis was performed by an accredited materials testing laboratory to determine if the sintering process used to produce the Ti-CP2 HVAI/sintered powder metal test specimens imparted any additional oxygen into the material. The analysis indicated that the sintering process did not impart additional oxygen into the test specimens. The average hardness of the Ti-CP2 HVAI/sintered test specimens was HRBW 96. This compares to an average hardness of HRGW 64 for the conventional Ti-CP2 wrought metal test specimen. Elongation for the Ti-CP2 HVAI/sintered test specimens was 7%, which is comparable to the elongation of Ti-CP2 powder metal components formed using conventional isostatic pressing/sintering processes, and compares to an average elongation of 22% for the conventional Ti-CP2 wrought metal test specimen. The differences in hardness and elongation for the Ti-CP2 HVAI/sintered test specimens versus the conventional Ti-CP2 wrought metal test specimen illustrate the effect of improved mechanical properties that result from the disclosed HVAI technique.

Advantageously, all powder metal Ti64 and Ti-CP2 test specimens formed by the disclosed HVAI/sintering regime exhibited a material density of approximately 99.5% of theoretical (wrought density). This correlates to significant improvement of mechanical properties as evidenced by the data presented herein.

Accordingly, a technique to increase the strength of metals and metal components has been disclosed. While various embodiments of the invention have been described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the invention. It is understood, therefore, that the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents. 

What is claimed is:
 1. A method for increasing the strength of metals or metal components, comprising: selecting a wrought metal or powder metal sample; said sample having a mass equal to or greater than a final mass of a component to be formed; if said sample is a wrought metal sample: placing said wrought metal sample in a die cavity incorporating geometric features of said component to be formed; subjecting said wrought metal sample in said die cavity to high velocity adiabatic impact; said high velocity adiabatic impact forming said wrought metal sample into a component having greater mechanical strength than said wrought metal sample prior to receiving said high velocity adiabatic impact; if said sample is a powder metal sample: placing said powder metal sample in a die cavity incorporating geometric features of a green preform to be created; subjecting said powder metal sample in said die cavity to high velocity adiabatic impact to form said green preform; sintering said green preform in a substantially oxygen free environment to form a sintered preform; and said sintered preform having greater mechanical strength than a wrought metal sample of the same material that has not received high velocity adiabatic impact.
 2. The method of claim 1, wherein said wrought metal or power metal sample comprises titanium.
 3. The method of claim 1, wherein said sample is a wrought metal sample.
 4. The method of claim 1, wherein said sample is a wrought metal sample comprising Ti64 titanium alloy and said component has a mechanical strength at least approximately 21% greater than said wrought metal sample prior to receiving said high velocity adiabatic impact.
 5. The method of claim 1, wherein said sample is a powder metal sample.
 6. The method of claim 1, wherein said sample is a powder metal sample and said green preform has a density in excess of 95% of a wrought metal sample of the same material.
 7. The method of claim 5, wherein said powder metal sample comprises Ti64 titanium alloy and said sintered preform has a mechanical strength at least approximately 27-32% greater than a wrought metal sample of the same material that has not received high velocity adiabatic impact.
 8. The method of claim 5, wherein said powder metal sample comprises Ti-CP2 commercially pure titanium and said sintered preform has a mechanical strength at least approximately 71-94% greater than a wrought metal sample of the same material that has not received high velocity adiabatic impact.
 9. The method of claim 5, wherein no isostatic pressing is performed prior to, during or after said sintering.
 10. The method of claim 1, wherein said sample is a powder metal sample, and wherein said method further includes: placing said sintered preform in a die cavity incorporating geometric features of said component to be formed; and subjecting said sintered preform in said die cavity to high velocity adiabatic impact to form said component.
 11. A method for increasing the strength of metals or metal components, comprising: selecting a wrought metal sample; said wrought metal sample having a mass equal to or greater than a final mass of a component to be formed; placing said wrought metal sample in a die cavity incorporating geometric features of said component to be formed; subjecting said wrought metal sample in said die cavity to high velocity adiabatic impact; and said high velocity adiabatic impact forming said wrought metal sample into a component having greater mechanical strength than said wrought metal sample prior to receiving said high velocity adiabatic impact.
 12. The method of claim 11, wherein said wrought metal sample comprises titanium.
 13. The method of claim 11, wherein wrought metal sample comprises Ti64 titanium alloy and said component has a mechanical strength at least approximately 21% greater than said wrought metal sample prior to receiving said high velocity adiabatic impact.
 14. A method for increasing the strength of metals or metal components, comprising: selecting a powder metal sample; said powder metal sample having a mass equal to or greater than a final mass of a component to be formed; placing said powder metal sample in a die cavity incorporating geometric features of a green preform to be created; subjecting said powder metal sample in said die cavity to high velocity adiabatic impact to form said green preform; sintering said green preform in a substantially oxygen free environment to form a sintered preform; and said sintered preform having greater mechanical strength than a wrought metal sample of the same material that has not received high velocity adiabatic impact.
 15. The method of claim 14, wherein said green preform has a density in excess of 95% of a wrought metal sample of the same material.
 16. The method of claim 14, wherein said powder metal sample comprises titanium.
 17. The method of claim 14, wherein said powder metal sample comprises Ti64 titanium alloy and said sintered preform has a mechanical strength at least approximately 27-32% greater than a wrought metal sample of the same material that has not received high velocity adiabatic impact.
 18. The method of claim 14, wherein said powder metal sample comprises Ti-CP2 commercially pure titanium and said sintered preform has a mechanical strength at least approximately 71-94% greater than a wrought metal sample of the same material that has not received high velocity adiabatic impact.
 19. The method of claim 14, wherein no isostatic pressing is performed prior to, during or after said sintering.
 20. The method of claim 14, wherein said method further includes: placing said sintered preform in a die cavity incorporating geometric features of said component to be formed; and subjecting said sintered preform in said die cavity to high velocity adiabatic impact to form said component. 